Percolation sheet

ABSTRACT

A percolation sheet  1  is constituted of a laminated sheet comprising a long-fiber nonwoven fabric  2  with a basis weight of 5 to 30 g/m 2 , at least a portion of which is formed from synthetic fibers of a high-melting-point resin, and a short-fiber nonwoven fabric  3  with a weight of 3 to 15 g/m 2 , at least a portion of which is formed from synthetic fibers of a low-melting-point resin. The short-fiber nonwoven fabric  3  is formed from a nonwoven fabric in which fibers with a fiber length of 3 to 15 mm are randomly dispersed and deposited using a dry process, and these fibers are thermally bonded to each other. In a diagram illustrating the relationship between the pore size of the voids in the percolation sheet and the distribution rate thereof, the distribution rate of the maximum peak is ten times or more of the distribution rate of the other peaks.

TECHNICAL FIELD

The present invention relates to a percolation sheet for use in theextraction of permeable (or extractable) raw materials such as blacktea, coffee, green tea, traditional Chinese medicines and the like.

BACKGROUND ART

In the case of percolation sheets used for the extraction of effusible(or extractable) raw materials such as black tea, coffee, green tea,traditional Chinese medicines and the like, good percolationcharacteristics with respect to the extract are required. Furthermore,in the case of percolation sheets that are used in the form of tea bags,it is necessary that the sheet have properties that allow bagmanufacture, that is, it must be possible to manufacture bags easilyusing a heat-sealing machine.

Conventionally, therefore, nonwoven fabrics made of synthetic fibers, inwhich the fibers themselves have low hygroscopicity and good percolationcharacteristics, have been used as percolation sheets. Furthermore, asheet manufactured by laminating a spun-bonded nonwoven fabricconstituted of polyester fibers with a high-melting-point and a cardednonwoven fabric constituted of polyester fibers with a low-melting-point(Flouveil (tradename) manufactured by OHKI Co., LTD.) is known as apercolation sheet that is suitable for bag-manufacturing. In the case ofthis percolation sheet formed by laminating a high-melting-pointspun-bonded nonwoven fabric and a low-melting-point carded nonwovenfabric, heat-sealing can easily be accomplished without any fusion ofthe fibers to the heating head of the heat-sealing machine bysuperimposing the two percolation sheets with the low-melting-pointcarded nonwoven fabric on the inside, and placing the superimposedsheets in a heat-sealing machine.

However, in a conventional percolation sheet formed by laminating aspun-bonded nonwoven fabric and a carded nonwoven fabric, the fibers ofthe carded nonwoven fabric are oriented in a specified direction that isdetermined by the carding machine, and are not uniformly dispersed inrandom directions. Consequently, the pore size distribution of the voidsin the nonwoven fabric extends over a broad range. Accordingly, if thebasis weight of the percolation sheet is adjusted so that a desirableliquid passage rate is obtained, fine particles of the permeable rawmaterial may pass through the percolation sheet. On the other hand, ifit is attempted to prevent the passage of fine particles of thepermeable raw material completely, the liquid passage rate shows anextreme drop.

Furthermore, in the case of a conventional percolation sheet formed bylaminating a spun-bonded nonwoven fabric and a carded nonwoven fabric,if the sealing width along the rim portion of the tea bag is narrowed inresponse to the recent market demand for a narrowing of this sealingwidth from the conventional value of approximately 5 mm to a value ofapproximately 2 mm, areas with a low sealing strength are generated inthe sealing parts, since the fibers of the carded nonwoven fabric thatperform a sealing function are oriented in a specified direction, andare not uniformly dispersed in random directions.

In regard to such problems, it is an object of the present invention toprevent the generation of areas with a low sealing strength in thesealing parts even in cases where the sealing width is narrowed, and toprevent the passage of fine particles of the permeable raw materialwhile maintaining a desirable liquid passage rate during the extractionof the permeable raw material.

DISCLOSURE OF THE INVENTION

The present inventor discovered that if the low-melting-point nonwovenfabric in a percolation sheet formed by laminating a high-melting-pointnonwoven fabric and a low-melting-point nonwoven fabric is constitutedof a nonwoven fabric in which short fibers are randomly dispersed anddeposited by a dry process and these fibers are thermally bonded to eachother at the intersection points thereof, the uniform dispersion of theshort fibers in random directions makes it possible to achieve heatsealing at a uniform strength in all portions of the nonwoven fabric.Furthermore, the present inventor also discovered that since the poresize distribution of the voids in such a nonwoven fabric is concentratedin an extremely narrow range, there are no voids that have anexcessively large pore size with respect to the desired void pore size,so that the passage of fine particles of the permeable raw materialduring the extraction of the permeable raw material can be prevented.

Specifically, the present invention provides a percolation sheet whichis formed by laminating a long-fiber nonwoven fabric with a basis weightof 5 to 30 g/m², at least part of which is formed from synthetic fibersof a high-melting-point resin, and a short-fiber nonwoven fabric with abasis weight of 3 to 15 g/m², at least a portion of which is formed fromsynthetic fibers of a low-melting-point resin, wherein the short-fibernonwoven fabric is formed from a nonwoven fabric in which fibers with afiber length of 3 to 15 mm are randomly dispersed and deposited using adry process, and are thermally bonded to each other, and in the diagramillustrating the relationship between the pore size of the voids in thepercolation sheet and the distribution rate thereof, the distributionrate of the maximum peak is ten times or more of the distribution rateof the other peaks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of the percolation sheet of the presentinvention;

FIG. 2(a) shows a photograph that illustrates the orientation of thefibers in an air-laid nonwoven fabric and FIG. 2(b) shows a photographthat illustrates the orientation of the fibers in a carded nonwovenfabric;

FIG. 3 is an explanatory diagram of the sealing strength test method;

FIG. 4 is a diagram of the pore size distribution of the voids in thepercolation sheet of Example 1;

FIG. 5 is a diagram of the pore size distribution of the voids in thepercolation sheet of Comparative Example 1; and

FIG. 6 is a diagram of the pore size distribution of the voids in thepercolation sheet of Comparative Example 2.

FIG. 7 is a diagram of the pore size distribution of the voids in thepercolation sheet of Example 2.

FIG. 8 is a diagram of the pore size distribution of the voids in thepercolation sheet of Example 2.

FIG. 9 is a diagram of the pore size distribution of the voids in thepercolation sheet of Example 2.

FIG. 10 is a diagram of the pore size distribution of the voids in thepercolation sheet of Example 2.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in detail below with referenceto the figures.

FIG. 1 shows the percolation sheet 1 of one aspect of the presentinvention; this percolation sheet has a laminated structure in which along-fiber nonwoven fabric 2 and a short-fiber nonwoven fabric 3 arelaminated.

Of these nonwoven fabrics, at least one portion of the long-fibernonwoven fabric is formed from synthetic fibers of a high-melting-pointresin, and preferably, at least one portion of this long-fiber nonwovenfabric is formed from synthetic fibers of a high-melting-point resinwith a melting point of 170° C. or higher. As a result, when the twopercolation sheets are superimposed with the short-fiber nonwoven fabricon the inside and placed in a heat-sealing machine, fusion of the fibersto the heating head of the heat-sealing machine can be prevented.

The reference to at least a portion of the long-fiber nonwoven fabricbeing formed from synthetic fibers of a high-melting-point resin with amelting point of 170° C. or higher includes cases in which the syntheticfibers that form the long-fiber nonwoven fabric are constituted only ofa synthetic resin with a melting point of 170° C. or higher, cases inwhich these synthetic fibers is constituted of mixed fibers constitutedof a synthetic resin with a melting point of 170° C. or higher andfibers constituted of a synthetic resin with a melting point of lessthan 170° C., and cases in which these synthetic fibers are constitutedof fibers with a core-sheath structure in which at least the surfacelayer (sheath) is formed from a synthetic resin with a melting point of170° C. or higher.

For instance, high-melting-point polyesters (high-melting-pointpolyethylene terephthalates: melting point 245° C.), polyamides (nylon66: melting point 245° C.), polyphenyl sulfides (melting point 290° C.),polylactic acids (melting point 178° C.) and the like may be cited asexamples of synthetic resins with a melting point of 170° C. or higher.

From the standpoint of the stability of the basis weight of the nonwovenfabric, it is desirable that the fiber diameter of the synthetic fibersthat form the long-fiber nonwoven fabric be 3 μm or less.

Methods that can be used to convert such synthetic fibers into anonwoven fabric include melt-blowing and the like; however, spun-bondingis desirable from the standpoint of obtaining a high strength withoutcausing clogging.

Furthermore, the basis basis weight of the long-fiber nonwoven fabric isset at 5 to 30 g/m². If the basis weight is less than 5 g/m², thestrength is insufficient; conversely, if the basis weight exceeds 30g/m², the percolation characteristics and mechanical suitability suffer,so that such a high basis weight is undesirable.

Meanwhile, in the percolation sheet of the present invention, at leastone portion of the short-fiber nonwoven fabric is formed from syntheticfibers of a low-melting-point resin, and preferably, at least oneportion is formed from synthetic fibers of a low-melting-point resinwith a melting point of 80° C. or greater but less than 170° C. As aresult, heat sealing can easily be accomplished by superimposing the twopercolation sheets with the short-fiber nonwoven fabric on the inside,and placing the superimposed sheets in a heat-sealing machine.

The reference to at least one portion of the short-fiber nonwoven fabricbeing constructed from synthetic fibers of a low-melting-point resinwith a melting point of 80° C. or greater but less than 170° C. includescases in which the synthetic fibers that form the short-fiber nonwovenfabric are constituted only of a synthetic resin with a melting point of80° C. or greater but less than 170° C., cases in which these syntheticfibers are constituted of mixed fibers formed from a synthetic resinwith a melting point of 80° C. or greater but less than 170° C. andother fibers, and cases in which these synthetic fibers are constitutedof fibers with a core-sheath structure in which at least the surfacelayer is formed from a synthetic resin with a melting point of 80° C. orgreater but less than 170° C. In particular, the use of fibers with acore-sheath structure is desirable from the standpoint of preventing thecrushing of the voids in the nonwoven fabric when the long-fibernonwoven fabric and short-fiber nonwoven fabric are joined. Furthermore,from the standpoint of increasing the joining strength of the long-fibernonwoven fabric and short-fiber nonwoven fabric, it is desirable to usethe same type of resin for the fibers that form the long-fiber nonwovenfabric and the fibers that form the short-fiber nonwoven fabric.Especially in cases where fibers with a core-sheath structure are used,it is desirable to use the same type of resin for the surface layers(sheaths) of the respective fibers.

For instance, low-melting-point polyesters (low-melting-pointpolyethylene terephthalates, melting point 100 to 160° C.),polyethylenes (melting point 90 to 140° C.), polypropylenes (meltingpoint 160 to 168° C.) and the like may be cited as examples of syntheticresins with a melting point of 80° C. or greater but less than 170° C.

Furthermore, fibers in which the core/sheath is formed from ahigh-melting-point polyester/low-melting-point polyester,high-melting-point polyester/polyethylene, polypropylene/polyethylene orthe like may be cited as examples of fibers with a core-sheathstructure.

The fiber length of the synthetic fibers that form the short-fibernonwoven fabric is set at 3 to 15 mm, preferably 5 to 7 mm. If the fiberlength is too short, the strength of the nonwoven fabric drops;furthermore, the fiber density is increased so that the liquid passagerate is slowed. Conversely, if the fiber length is too long, it becomesdifficult to achieve a uniform dispersion of the fibers.

The fiber diameter of the synthetic fibers that form the short-fibernonwoven fabric also depends on the pore size distribution desired forthe percolation sheet in accordance with the permeable raw material.However, in cases where (for example) the percolation sheet is used incommon tea bags for black tea, the fiber diameter is preferably set at0.1 to 3.0 d (denier), and is even more preferably set at 0.5 to 2.0 d.If the fiber diameter is too small, the pore size of the nonwoven fabricwill be reduced, so that the liquid passage rate is slowed. Conversely,if the pore size is too large, fine particles of the permeable rawmaterial such as black tea or the like will pass through the nonwovenfabric, so that the taste and appearance of the extracted liquid suffer.

In regard to the method used to form such synthetic fibers into anonwoven fabric, first a web is formed by randomly dispersing anddepositing the fibers using a dry process; then, a nonwoven fabric isformed by thermally fusing the fibers to each other at the intersectionpoints thereof. In more concrete terms, a web is formed by theair-laying method, and this web is heat-treated using an embossing roll,flat roll or the like.

In the web formed by the air-laying method, the fibers are dispersedwith a uniform thickness in random directions. Furthermore, theuniformity of the dispersion of the fibers is not impaired even if thisweb is heat-treated with an embossing roll or the like. Accordingly, inthe short-fiber nonwoven fabric formed in this manner, the pore sizedistribution is concentrated on a narrow range. In the diagramillustrating the relationship between the pore size of the voids in thepercolation sheet and the distribution rate thereof, the distributionrate of the maximum peak is ten times or more of the distribution rateof the other peaks. The pore size distribution shows a dispersion rangeof preferably 100 μm or less, more preferably 50 μm or less, and shows asingle peak. Furthermore, the term “pore size distribution” used in thepresent invention refers to a distribution measured by the bubble pointmethod (JIS K3832).

Furthermore, the pore size distribution of the short-fiber nonwovenfabric formed in this manner can be sharply controlled by adjusting thefiber diameter and basis weight of the nonwoven fabric.

Furthermore, a nonwoven fabric in which the fibers are dispersed inrandom directions can also be obtained using a papermaking process,which is a wet process; however, the air-laying method is preferablefrom the standpoint of productivity.

In regard to the method used to laminate the long-fiber nonwoven fabricand short-fiber nonwoven fabric in the present invention, a method maybe used in which the long-fiber nonwoven fabric and short-fiber nonwovenfabric are separately formed, after which both are superimposed andlaminated by performing a heat treatment using an embossing roll, flatroll or the like; alternatively, a method may be used in which a webthat forms the short-fiber nonwoven fabric is formed onto the long-fibernonwoven fabric, and a heat treatment is applied to this using anembossing roll, flat roll or the like so that the conversion of the webthat forms the short-fiber nonwoven fabric and the lamination andbonding of the short-fiber nonwoven fabric and long-fiber nonwovenfabric are performed simultaneously.

In the percolation sheet of the present invention, a low-melting-pointshort-fiber nonwoven fabric and a high-melting-point long-fiber nonwovenfabric are laminated, and the pore size distribution of the short-fibernonwoven fabric is concentrated on a narrow range. On the other hand,the pore sizes of the long-fiber nonwoven fabric are large. Accordingly,with respect to the pore size distribution of the percolation sheet as awhole, in the diagram illustrating the relationship between the poresize of the voids in the percolation sheet and the distribution ratethereof, the distribution rate of the maximum peak is ten times or moreof the distribution rate of the other peaks, and the pore sizedistribution shows a dispersion range of preferably 100 μm or less, morepreferably 50 μm or less, and shows a single peak. Consequently, adesirable liquid passage rate can be ensured, and the passage of fineparticles of the permeable raw material through the percolation sheetcan be prevented during the extraction of the permeable raw material.Furthermore, since the low-melting-point fibers of the short-fibernonwoven fabric which bears the bonding characteristics that arerequired when the percolation sheet is heat-sealed are dispersed at auniform thickness in random directions, heat sealing with a uniformstrength can be accomplished in all parts of the nonwoven fabric.Accordingly, even if the sealing width is narrow, areas of insufficientstrength are not generated in the sealed portions. Consequently, thepercolation sheet of the present invention is extremely useful as asheet material for forming tea bags used for permeable raw materialssuch as black tea, coffee, green tea, traditional Chinese medicines andthe like.

Besides a sheet which has a laminated structure constituted of along-fiber nonwoven fabric 2 and short-fiber nonwoven fabric 3 as shownin FIG. 1, other woven fabrics, nonwoven fabrics or the like may also belaminated if necessary in the percolation sheet of the presentinvention. For example, a bonding nonwoven fabric may be disposedbetween the long-fiber nonwoven fabric and short-fiber nonwoven fabricin order to increase the bonding strength thereof.

EXAMPLES

The present invention will be concretely described below in terms ofembodiments.

Experiment 1

A web was formed by the air-laying method using fibers (fiber diameter1.0 d, fiber length 5 mm) with a core-sheath structure in which thecore/sheath constituted of a high-melting-point polyethyleneterephthalate/low-melting-point polyethylene terephthalate, and anair-laid nonwoven fabric was manufactured by applying a heating roll.Meanwhile, a carded nonwoven fabric was manufactured using similarfibers. Then, ten samples with dimensions of 9.0 cm×6.0 cm and tensamples with dimensions of 100 cm×100 cm were cut from the respectivenonwoven fabrics, and the basis weight of the samples was measured. Theresults obtained are shown in Tables 1 and 2. Furthermore, a photographof the air-laid nonwoven fabric is shown in FIG. 2 (a), and a photographof the carded nonwoven fabric is shown in FIG. 2 (b). TABLE 1 Air-laidnonwoven Carded nonwoven Sample fabric fabric No. [g/9.0 cm × 6.0 cm][g/9.0 cm × 6.00 cm] 1 0.044 0.056 2 0.045 0.054 3 0.044 0.059 4 0.0430.057 5 0.044 0.055 6 0.044 0.056 7 0.045 0.059 8 0.44 0.057 9 0.440.055 10 0.44 0.058 Mean 0.044 0.057 Standard 0.00054 0.00162 deviation

TABLE 2 Air-laid nonwoven Carded nonwoven Sample fabric fabric No.[g/100 cm × 100 cm] [g/100 cm × 100 cm] 1 8.14 10.42 2 8.02 10.58 3 8.2910.32 4 8.23 10.12 5 8.15 10.71 6 8.31 10.44 7 8.22 10.28 8 8.16 10.41 98.07 10.35 10 7.99 10.40 Mean 8.16 10.40 Standard 0.10245 0.15238deviation

In Tables 1 and 2, a comparison of the standard deviations of theweights of the air-laid nonwoven fabric and the carded nonwoven fabricindicates that the air-laid nonwoven fabric shows very little variationin weight within the nonwoven fabric compared to the carded nonwovenfabric.

Furthermore, it is seen from FIGS. 2(a) and 2(b) that while the fibersare uniformly dispersed in random directions in the air-laid nonwovenfabric, the fibers are oriented in a fixed direction in the cardednonwoven fabric, so that there is some irregularity in the basis weight.

Example 1, Comparative Examples 1 and 2

A spun-bonded nonwoven fabric was manufactured using ahigh-melting-point polyester with a fiber diameter of 2.0 d. A web wasformed onto this nonwoven fabric by the air-laying method using fibers(fiber diameter 2.0 d, fiber length 5 mm) with a core-sheath structurein which the core/sheath were constituted of a high-melting-pointpolyethylene terephthalate/low-melting-point polyethylene terephthalate,and an embossing roll was applied thereto, so that a percolation sheetin which an air-laid nonwoven fabric (basis weight 6 g/m²) was laminatedon a spun-bonded nonwoven fabric (basis weight 12 g/m²) was manufactured(Example 1).

Meanwhile, a percolation sheet similar to the above in which a cardednonwoven fabric (basis weight 8 g/m²) was laminated on a spun-bondednonwoven fabric (basis weight 12 g/m²) was manufactured using the samefibers (provided that the fiber length is 51 mm) as those used in theair-laid nonwoven fabric (Comparative Example 1).

Furthermore, a percolation sheet was also manufactured in the samemanner as in Comparative Example 1, except that the embossing shape ofthe embossing roll was altered (Comparative Example 2).

Example 2

A percolation sheet, in which an air-laid nonwoven fabric (basis weight8 g/m²) was laminated on a spun-bonded nonwoven fabric, was alsomanufactured in the same manner as in Comparative Example 1, except thatthe air-laid nonwoven fabric has a basis weight 8 g/m².

Evaluation

(1) Test of Sealing Strength

The two percolation sheets of Embodiment 1 were superimposed with theair-laid nonwoven fabric on the inside, and were heat-sealed at a widthof 15 mm (heating temperature 150° C.). The heat-sealed sheets were thencut into a rectangular shape (15 mm×50 mm) as shown in FIG. 3, and theload at which the sealed part 4 peeled away when a peeling force wasapplied from the non-sealed side was determined. In FIG. 3, the numeral2′ denotes a spun-bonded nonwoven fabric and the numeral 3′ denotes anair-laid nonwoven fabric.

The percolation sheets of Comparative Example 1 were similarlysuperimposed and heat-sealed with the carded nonwoven fabric on theinside, and the load at which the sealed part peeled away wasdetermined.

The results obtained are shown in Table 3. Comparative Sample Example 1Example 1 No. [kg/15 cm] [g/100 cm × 100 cm] 1 0.22 0.46 2 0.22 0.68 30.23 0.37 4 0.21 0.39 5 0.21 0.41 6 0.22 0.70 7 0.24 0.62 8 0.23 0.33 90.20 0.41 10 0.23 0.54 Mean 0.22 0.49 Standard 0.10245 0.15238 deviation

It is seen from Table 3 that the percolation sheet of Example 1 showsvery little variation in sealing strength compared to the percolationsheet of Comparative Example 1.

(2) Pore Size Distribution

The pore size distributions of the voids in the respective percolationsheets of Example 1, Example 2, Comparative Examples 1 and ComparativeExample 2 were measured by the bubble point method (JIS K3832) using aPerm-Porometer manufactured by U.S. PMI Co. The results obtained areshown in FIGS. 4 through 10. With respect to the percolation sheet ofExample 2, it was measured at 4 measurement points different from eachother in respect of a position in width direction (FIGS. 7 to 10).

It is seen from these figures that while the percolation sheets ofComparative Example 1 and Comparative Example 2 show a variation of morethan 140 μm in the pore size distribution, with a plurality of peaksbeing present in this range, the pore size distribution of thepercolation sheet of Example 1 shows a single peak in a variation rangeof less than 10 μm, so that the pore size distribution is concentratedin this range. With respect to the percolation sheet of Example 2, atany of the 4 measurement points, the distribution rate of the maximumpeak was ten times or more of the distribution rate of the other peaks,and the pore size distribution was concentrated on the maximum peak.

Industrial Applicability

The percolation sheet of the present invention makes it possible toachieve a conspicuous reduction in the variation of the sealing strengthin the sealed parts, even in cases where the sealing width is madenarrow. Furthermore, since the pore size distribution of the voids inthe nonwoven fabric can be sharply controlled, preferably made to be asingle peak, the passage of fine particles of the permeable raw materialthrough the percolation sheet can be prevented while maintaining adesirable liquid passage rate during the extraction of the permeable rawmaterial.

1. A percolation sheet which is formed by laminating a long-fibernonwoven fabric with a basis weight of 5 to 30 g/m², at least part ofwhich is formed from synthetic fibers of a high-melting-point resin, anda short-fiber nonwoven fabric with a weight of 3 to 15 g/m², at least aportion of which is formed from synthetic fibers of a low-melting-pointresin, wherein the short-fiber nonwoven fabric is formed from a nonwovenfabric in which fibers with a fiber length of 3 to 15 mm are randomlydispersed and deposited using a dry process, and are thermally bonded toeach other, and in a diagram illustrating the relationship between thepore size of the voids in the percolation sheet and the distributionrate thereof, the distribution rate of the maximum peak is ten times ormore of the distribution rate of the other peaks.
 2. The percolationsheet according to claim 1, wherein the pore size distribution shows adispersion range of 100 μm or less and shows a single peak.
 3. Thepercolation sheet according to claim 1, wherein the melting point of thehigh-melting-point resin is 170° C. or greater, and the melting point ofthe low-melting-point resin is 80° C. or greater but less than 170° C.4. The percolation sheet according to claim 1, wherein the fibers thatform the short-fiber nonwoven fabric have a core-sheath structure inwhich the surface layer is formed from a low-melting-point polyester andthe core is formed from a high-melting-point polyester.